Some control systems for air-operated devices utilize normally open solenoid valves that are turned on and off by electric switches. A problem with these systems is that a loss of power to the solenoid valves, for any reason, may cause an undesirable change in the state of the air in the system. For example, some trucks are provided with an air-operated suspension system. The driver of the truck may wish to park the truck at a loading dock, dump the air in the suspension system, and at the same time turn off the ignition and leave the truck in this state for a long period of time. In the conventional air/electric system, turning off the ignition would cause the solenoid valve that dumps the air to become de-energized, causing the suspension system to return to a suspended position. It is not a viable option to leave the solenoid energized indefinitely because this would result in an undesirable drain of the battery in the truck. There is a need to overcome the stated problem by providing an air signal that does not change state when electric power is lost or removed. The primary object of this invention is to fill this need.